If looking at a dashboard wasn't a disadvantage they'd be already doing that. There would be no need for banning simpler and better way of someone informing you over the radio. Ask Rosberg in China when he had to read out numbers if it's not distracting.
I don't see any of this as really important and as always there are questions of why they're doing it now in the middle of the season. If everyone uses it, cumulated gain is zero and performance higher. Cumulated meaning that not for all equally: for some driver it might be important in the race (the one with higher fuel consumption) and for the other not. One would have to look at the display and the other not thus making stupid fuel consumption or brake temperatures even more important.
What about failure events like Perez in Canada or Monza when his sensor failed and his engine was below 100% for three(?) laps. So on top dealing with worse performance he can't hear any information about adjustment of the car and driving to that? Brilliant, pure racing and another area for random stewarding and special circumstances for some.
Edit: Oh look clarification needed, no s.. sherlock.
http://www.gpupdate.net/en/f1-news/3160 ... trictions/ "This is a complex and controversial decision which will require a significant effort from the teams to understand how best we can work around it," said Wolff, who is the first team boss to share his thoughts on the rule change.
"The directive is not yet fully clear and there will inevitably be some controversy, so it will need further clarification as to how much the essential on-track procedures will be affected – particularly before the start of the race."